Folding of car seat backrests is commonly performed to provide a more or less flat surface that can be used as a bed. Obviously, when the seat backrest is folded backwards the seat cushion is left somewhat lower than the plane defined by the former, so that the bed will not be comfortable to lie on.
In this sense, systems or mechanisms are known that allow folding a car seat backrest backwards and also slightly raising the seat cushion to improve the horizontal plane of the assembly; this is, to provide a horizontal or aligned surface between the upper part of the cushion and the upper part of the backrest when the latter is folded backwards.
An example of a mechanism that allows folding the seat backrest backwards and raising its cushion to form a bed is provided in U.S. Pat. No. 6,135,558 in which an arched part in the form of a connecting rod is disposed between the seat cushion and the backrest which is tilted when folding the backrest backwards, thereby raising the rear part of the cushion, the front part of which is also lifted by a set of connecting rods hinged to each other as well as to the seat cushion and to the fixed structure of the seat.
The mechanism is completed by locking means to maintain stability both in the normal position of the backrest and in its folded position, in order to stabilise these positions as mentioned.
In any case, this mechanism has drawbacks such as the need for two connecting rods and their corresponding hinges to raise the front part of the cushion as the backrest is folded backwards, as well as the need to use a hinged rod to connect the cushion with the backrest in spite of the poor reliability of the arching means between the stable resting and folded positions.
Other mechanisms are described in documents such as German Patent DE 10035256 C1, U.S. Pat. No. 4,268,086, European Patent EP 0628445 A1, among others, although all have the disadvantage that the mechanisms used to transform the car seat into a bed are complex, as they comprise a great number of parts with the resulting drawbacks.